The present invention relates generally to radio resource management in a wireless communication system. Specifically, the present invention relates to a method and apparatus for generating downlink power information for a multi-sector base transceiver site in which power can be shared between the sectors. Such information can be used in radio resource management in a wireless communication system.
In wireless communication systems, a user device, which is typically mobile, is in wireless communication with a base transceiver station, which generally provides a communication connection to other user devices in wireless communication with the base transceiver station, or with other user devices attached to a communication system to which the base transceiver station belongs, such as a cellular communication system, or with an external network such as the public switched telephone network (PSTN) or the Internet for example. The direction from the user device to the base transceiver station is called uplink and the direction from the base transceiver station to the user device is called downlink.
In general, a base transceiver station has a receive section and a transmit section. The receive section receives uplink radio frequency signals from the user device via an antenna, mixes the received radio frequency signal to obtain a base band signal and demodulates/decodes the resulting base band signal to obtain the received data, for example signaling or message data or user data for onward transmission to a destination, for example via a cellular communication system to which the base transceiver station belongs to another user device.
The transmit section receives data for transmitting to a user device in contact with the base transceiver station, modulates/codes the data to obtain a base band signal for the user, and then mixes the base band signal to receive an radio frequency signal for the user. The radio frequency signal for the base transceiver station, i.e. the cumulative radio frequency signal for all user devices, is then amplified by a power amplifier prior to being transmitted via the base transceiver station antenna.
In order to increase capacity in the communication system, a base transceiver station site may be sub-divided into separate sectors or cells, each of the sectors or cells being provided with a separate power amplifier and antenna. In this situation it has been found to be advantageous to pool the power amplifier resources of the sectors of a multi-sector base transceiver station.
This can be achieved by sharing signals to be amplified for each sector across all of the power amplifiers i.e. N input signals are split and are then recombined into N new signals after amplification by the power amplifiers.
This arrangement enables the required dynamic range of each of the power amplifiers to be reduced, as the signal amplification is shared across a pooled resource of power amplifiers, leading to a reduction in cost of the power amplifiers. This is particularly important in Code Division Multiple Access (CDMA) systems due to the inherently large dynamic range of the resulting aggregate signal, which requires linear amplification. In addition, this arrangement provides automatic power amplifier redundancy, since failure of one of the power amplifiers will not result in a sector losing all power amplification. Finally, this arrangement can enable power sharing between different systems, e.g. AMPS and IS95 systems, where the base transceiver stations are co-located.
In general, the radio resources available to a base site are finite, and are divided by frequency and/or time and/or codes into a number of physical and logical channels, according to the wireless technology employed. A base transceiver station typically supports a number of user devices, and therefore the radio resources i.e. the different channels available to the base station must be allocated to the different user devices. In general, this allocation is handled by a Radio Resource Management function.
In many systems, some Radio Resource Management functions may depend at least partially on the total power available per cell. This is particularly true of Code Division Multiple Access (CDMA) systems, in which downlink Radio Resource Management functions such as admission control and scheduling of users is generally based on the number of code channels available and on the total transmit power available per cell. In most CDMA systems, the number of orthogonal codes available is sufficient and does not generally impose a limitation. Therefore, the system capacity is limited by the maximum transmit power capability of the cell, which in turn is governed by the rated power of the base transceiver station power amplifier.
The Radio Resource Management function generally relies on power measurements from the base transceiver station, in particular the per user code power and the total transmit carrier power to determine how close each individual cell is to the maximum capacity of the cell i.e. the rated power of the amplifier.